Household appliances such as dish washers, washing machines, refrigerators and automatic ovens are becoming ever more sophisticated in their use of timing and control devices. In the commercial area, too, vending machines, amusement machines and the like are also using more complex controls. The many advances in logic circuit design and fabrication resulting from the growth of computer and space related technologies has made available quite complex logic circuits in relatively small, low cost packages such as provided in MOS and other integrated circuit forms. These logic circuits are quite appealing as substitutes for larger, more expensive electrical and electro-mechanical mechanisms used in these devices.
However, there is a serious problem in the application of these circuits to such devices: the final output of these circuits, which is quite low in power, must drive heavy equipment e.g., motors. Obviously such circuits cannot accomplish this without some interface to buffer the low power output circuits to the high power input equipment. An SCR semiconductor switch or a TRIAC may be and is used for this purpose. However TRIAC's and SCR's are quite expensive and have an inherent voltage offset, typically one volt, that causes internal power dissipation which limits the current they can pass.